Rubber to metal adhesive and method of making same



Patented Jilly 10.1945

vireo STATES PATENT OFFICE RUBBER TO AND This invention relates to rubber to a method of preparing the same.

larly relates to an ing rubber to meted.

METHOD OF MAKING SAME Roy Vance and Clement A. Damicone, Akron,

hi0, assignors to The Company, Akron, Ohi

No Drawing. Applica General Tire tion September &. Rubber a corporation of Ohio Serial No. 457,328 4 Claims. (Cl. Mil-#769) derivatives and It particuimproved adhesive for adher- (Fe-pending applications of Thomas Raymond Grifiith, Serial No. 277,086, filed June 2, 1939, and

identical properties.

It is a further objec t of the present invention to isomer or rubber derivative of uniform properties an tometal with great strength at d capable of bonding rubber" both normal and elevated temperatures. Y

It is a still further object of the present inthe metal with high s \l have found that omposite articles of rubber trength. these and other objects,

whichwillbe apparent from the following detailed description -of the inv ention, are accomplished by render it soluble in rubber solvents. In order to increase age resistance and heat resistance, it is also desirable to add a small amount of sulphur or selenium, or both, to the not masticated to a v rubber or mixture "prior to the reaction.

We are of course aware of the disclosure in the above mentioned Grifiith applications to the effect that alums in conjunction with a weak acid such as phosphoric anhydride may be used in place of the aluminum acid sulfate P205 and water in forming desirable rubber derivatives. We are not aware of any disclosure however which discloses the proportion of alums and P205 which we have, as hereinafter more fully described,'found to produce a more uniform and more desirable product.

Neither are Weaware ofQany disclosure of the use of a conversion or cyclizing agent comprising a small amount of a strong mineral acid, particularly sulfuric acid in addition to an alum and weak acidic ingredients. We have found that a small amount of the strong acid further improves the characteristics of the rubber derivative.

We have also concluded from the results of our experiments that it is undesirable to add water, as

5 water, to the rubber for the reason that the startrubber is always bonded to (by weight) of alum for ing period of the reaction does not appearto be controllable when water is added in this manner. When all of the water is added as water of crystallization in a compound such as alum, which and the cyclizing reaction appears to commence at a definite temperature so that duplicative results are obtainable.

The alums which are found to be desirable for use in accordance with the present invention are containing twenty-four and A12 (S04) 3.N3.2SO4.24H2O are preferred, although iron, ammonium iron, etc;, also may be used.

The hardness of the conversion product or the rubber derivative depends in large measure on the amount of the conversion for rubber-to-metal adhesive, at least fifteen parts than fifteen parts,.the

other alums such as 110- tassium chrome, potassium manganese, potassium ent in amounts between 18 and ture rises too gen in the air,

to bond with any strength. When more than thirty parts of alum are present inthe mix, the product becomes so hard that the adhesion of rubber to metal is inefflcient. For rubber-tometal adhesives suitable for bonding'rubber to metal with a single coat, and for producing the strongest bonds, the alum should usually be pres- 25 parts for each one hundred parts of rubber.

A substance such as phosphorus pentoxide (phosphoric anhydride), which with water forms weak acid constituent of the conversion or cyclizing agent. The amount of phosphorus pentoxide is less than the amount of alum and the preferred amount varies substantially with the amount of sulphuric acid present. sulphuric acid present, the amount of pentoxide may be as much as about eight parts for each one hundred parts of rubber. When the amount of sulphuric acid is increased, the desirable amount of phosphorus pentomde should be decreased but at least two or three parts is always desirable and about three preferred for each one hundred parts of rub Although a reaction product with good properties may be produced without the addition of any sulphuric acid, a small amount of sulphuric acid improves the characteristics and uniformity of the product for adhesives. It also permits the use of less phosphorus pentoxide than is otherwise necessary to produce a reaction product of the desired hardness for composite articles of rubber and metal. As little as 2% or .3% of concentrated sulphuric acid is eflective in improving the reaction mix; more than four or five parts of sulphuric acid has an undesirable effect on the character of the conversion or cyclized product. The sulphuric acid should preferably be less than the amount of weak acid anhydride and between about 1% and about 3% of the weight of the rubber is most desirable.

phosphorus with or without the addition of up to 3% sulphur. is preferably formed in a relatively thin section not substantially exceeding one-half inch and preferably less than one-fourth inch in thickness. The formation of the mixture in thin section is beneficial in facilitating the exothermic reaction and the time necessary for a complete reaction decreases as the thickness of the reaction product is decreased. When the thickness of the mixture is substantially over one-fourth inch or so in thickness, the complete reaction takes place with considerable diiliculty.

" Theconditionsduliing the heating considerably affect the, character of the exothermic reaction product. If the temperature of the mixhigh, the reaction product will be adversely affected; if the temperature is not sufficiently high or the time of heating is too short,

and the product is also adversely a eete When essp about one-eighth I have found that an esthe mixture has a thic inch to one-fpurtlfinch,

""pecially desirable product is obtained with a heating period of about one and a half to two hours at 300 F. oven temperature.

With very small amounts or no to flve parts are The mixture of rubber and conversion reagents,

action on the The reaction beinzasraoss creased, below atmospheric pressure, the reac- 6 tion time is increased and the uniformity of the product is increased. Withthan 20 or 22 inches of mercury, surface coatings of undesirable characteristics are substantially eliminated.

In the preparation of rubber-to-metal adhesives from the cyclized derivative or reaction product prepared as above described, the reaction product is masticated sufficiently to render it soluble in rubber solvents. Preferably during the mastication, the reaction product is suitably compounded with one or more ingredients capabl of neutralizing any acidic residue in the reaction An antioxidant and reinforcing pigment such as carbon black together with an accelerator is also preferably incorporated during When the mixture is masis soluble, it is prefa pressure of less the mastication step.

ticated sufficiently so that it erably immediately dissolved or dispersed in sufficient rubber solvent to obtain a cement of the desired consistency. Petroleum rubber solvents, such as gasoline containing about 3% to 5% butyl alcohol, are usually preferred, but aromatic solvents such as benzol (benzene) or mixtures containing aromatic rubber solvents also may be used.

In the T. R. Griffith application Serial No. 353,- 914, filed August 23, 1940, there is set forth a rubber-to-metal adhesive containing sulphur and/or other vulcanizing agents such as selenium and tellurium added to the solution of dissolved derivatives: We have also found aration of rubber-to-metal adhesives of derivatives of the present invention, additions of sulphur to the solution is desirable in improving heat resistance of the product in the same manner as set forth in the above Grimth application. At least 5% of sulphur, or equivalent vulcanizing agents, preferably are added'to the solution of the derivative. Best results are usually-obtainable with 10 or 15% of sulphur based upon the weight of the cyclized derivative.- Even more than 20% of sulphur may, however, be present in the adhesive without decreasing the strength of the bond. It is preferable to maintain the percentage below about 50% of sulphur.

The type of accelerator used in the adhesive is important in obtaining high bonding strength. Those accelerators which exert a stiffening or anti-plasticizing effect on solid rubber mixes are preferred. Such accelerators usually have one or more primary amino groups. plurality of primary amino groups 'suc for example as 2,4 diaminodiphenylamine, are especially desirable. The antioxidant should also preferably be-of atype which produces a stifiening rubber. Examples of desirable antioxidants are those of the Neozone series and the reaction does not appear to become cgnipleted bondensation products of acetone and aniline sold under the trade name Flechtol HQ However,

other antioxidants may also be used The following examples illustrate the present invention:

Example 1 I y Parts by weight Rubber masticated smoked sheets. (or

exothermic, the temperature in the reaction mix may rise to about 325 F. or so. The oven temper- 'm "quivalenti 100 atures should preferably be held betweemabout Potassium alum 2o 270 F. and 325 F. for best results. It is preferred Phosphorus pentoxide a.

to heat the mixture in an atmosphere having less Concentrated sulphuric acid 1% oxygen pressure than the partial pressure of oxy- Sulphur 1 such as obtained with an inert gas Selenium 3 formation of that in the'prep- Those having an/ one pound of masticated material Reaction product of Example 1 asvaase The above ingredients were suitably mixed on a rubber mill, and formed in a shape having thin section, such as $4," and A" or so. The thin sheets were then heated in a vacuum oven at about 20 inches of mercury and at about 300 F. for ninety minutes to procure a reaction product.

The sheets were spaced during the heating period to provide adequate circulation of air in the oven. The reaction product was a rubber derivative which had less plasticity than crude rubber at 120 (3., it had the same carbon-tohydrogen ratio as rubber but had less chemical unsaturation than a rubber addition product of the same chemical formula, thus indicating cyclization of the derivative, and indicating that the reagent is, with the aid of heat, a 'cyclizing agent for rubber.

Example 2 Parts by weight Antioxidant (condensation product of ,aoe-

tone and aniline) 2 Magnesium oxide 15 Zinc oxide 30 Carbon black (P33) 15 Red iron oxide (F6304) Accelerator (2.4 diaminodiphenylamine) 2 The above ingredients were mixed on a mill and mastication continued until the rubber derivative was solubilized. 174 parts of the masticated product were then dissolved in gasoline containing 3% of butyl alcohol in the ratio of for each gallon of solvent. 10.5 parts of sulphur and 3.5 parts of selenium were then thoroughly mixed into the solution toproduce a rubber-to-metal adhesive.

Composite articles of rubber and metal were made using the rubber-to-metal adhesive above prepared. The articles were made by applying a single coat of adhesive to a clean surface or the metal, allowing it to dry and then vuicanizing a suitable curable compounded coated surface under heat and pressure. The articles were removed from the mold without cooling the mold and when they were tested at room temperature the tensile strength of the bond between the rubber and metal was about 830 lbs. per sq. in.

When in the above Example 1 thesulphuric acid was omitted and the reaction product otherwise identically prepared, products produced with the cement prepared in accordance with Example 2 had a tensile strength of only 180 lbs. per sq. in. However, when the amount of phosphorus pentoxide was increased to 6%, sulphuric acid also being omitted, composite articles prepared had a bonding strength of 600 lbs. per sq. in. When the sulphuric acid was omitted and the amount of phosphorus pentoxide was increased to eight pounds, the composite articles prepared had a bonded strength of only 260 lbs. per sq. in. When in above Example 1 the amount of alum is reduced to parts, the product becomes so soft that the bond between the rubber and metal has but a little strength. on the other hand, when the amount of alum is increased to'more than 30 .parts, the resin becomes so hard that the strength of the bond is reduced The sulphur and/or below usable value. selenium may be omitted from Example 1 to produce a cyclized hydrocar-- bon rubber derivative or ,rubber isomer. The bydrocarbon product thus produced has lower heat resistance and slightly inferior aging properties than the products produced in accordance with Example 1. When the sulphur and selenium are I strength of the bond is rubber I against the usually somewhat decreased when subjected to high temperatures.

An even stronger bond than that disclosed above may be obtained if a suitable tie cement is applied to the rubber-to metal adhesive on the metal so that the tie cement is between the rubber-to-metal adhesive and the rubber to be bonded to the metal; The tie cement should preferably have as its solid organic base about equal parts of the compounded rubber-derivative and the rubber compound. Other proportions of these are sometimes desirable. A tie cement is usually unnecessary to obtain bonds of sufiicient strength for most applications.

While slightly masticated smoked or its equivalent is generally used in the prepara-. tion or rubber-to-metal adhesives, it

combined with an equivalent amount of added elements.

While the vulcanizing agenta' selenium, have been mainly emphasized throughthe term rubber elude derivatives ing or combining chemically It is to be understood that variations and modifications of the procedure herein shown and described for purposes of illustration may be made without departing from the spirit of the invention.

What we claim is:

l. A method of producingrubber derivatives oi: the cyclized type, as evidenced by having the same carbon-to-hydrogen ratio as rubber and having. less chemical unsaturation than rubber and unsaturated rubber addition products of the same percentage composition, which comprisesv forming a mixture of rubber, an alkali metal phosphorus pentoxide and freesulphuric mixture to procure an exothermic reaction product, said alum being 1 present in the mix in amounts between about 15 parts and about 30 parts for each parts: of

same carbon-to-hydrogen ratio as same percentage composition, which comprises forming a mixture of rubber, an alkali metal alum, phosphorus pentoxide, a vulcanizing agent sheet rubber v and even vulcanizing types of acand free sulphuric acid, and heating the mixture of rubber and wherein said mixtureis heated in to procure an exothermic reaction product, said an inert atmosphere to procure said reaction alum being present in the mix in amounts beproduct.

tween about 15 parts and about 30 parts for each 4. The method of claim 1 wherein said mix- .phorus pentoxide being between 2 parts and 8 temperature between 270 F. and 325 F. and in parts for each 100 parts of rubber, said sulphuric an atmosphere having less oxygen pressure than acid being present in amounts of .2 to 5 parts for the partial pressure of oxygen in the atmosphere. each 100 parts of rubber. ROY M. VANCE.

3. 'The method of claim 1 wherein the amount 10 CLEKENT A. DAMICONE. of sulphuric acid is 1 to 3 parts for each 100 parts 100 parts of rubber, the amount of said phos- 5 ture is heated in a form having thin section at a 

